Conventionally, microfabrication has been carried out using photolithography techniques in the production of semiconductor devices. The microfabrication is a fabrication process in which a thin film of a photoresist composition is formed on a substrate to be fabricated such as a silicon wafer, active rays such as ultraviolet rays are applied onto the film through a mask pattern with a pattern of a semiconductor device followed by development, and the substrate to be fabricated such as a silicon wafer is etched using the obtained photoresist pattern as a protective film. In recent years, semiconductor devices have been further integrated, and the active rays to be used have had a shorter wavelength from a KrF excimer laser (248 nm) to an ArF excimer laser (193 nm). Such a change raises serious problems due to the effects of irregular reflections of active rays from a substrate and standing waves. Thus, a method of providing a bottom anti-reflective coating (BARC) between the photoresist and the substrate as a resist underlayer film that suppresses the reflections has been widely employed.
Inorganic bottom anti-reflective coatings made of titanium, titanium dioxide, titanium nitride, chromium oxide, carbon, α-silicon, or other substances and organic bottom anti-reflective coatings composed of a light-absorbing substance and a polymer compound are known as the bottom anti-reflective coatings. The former needs equipment such as a vacuum deposition system, a CVD system, and a sputtering system for the coating formation, but the latter has advantages because special equipment is not required, and there have been many studies on the latter.
Examples of the organic bottom anti-reflective coatings include an acrylic resin bottom anti-reflective coating that includes a hydroxy group as a cross-linkable group and a light-absorbing group in a single molecule (see Patent Document 1) and a novolac resin bottom anti-reflective coating that includes a hydroxy group as a cross-linkable group and a light-absorbing group in a single molecule (see Patent Document 2).
It is described that physical properties required for the organic bottom anti-reflective coating material are, for example, large absorption of light and radiation rays, no intermixing with a photoresist layer (being insoluble in a resist solvent), no diffusion of a low molecular weight compound from a bottom anti-reflective coating material into a resist applied on the bottom anti-reflective coating during application or drying by heat, and a dry etching rate larger than that of a photoresist (see Non-patent Document 1).
In recent years, as a next-generation photolithography technique subsequent to the photolithography technique using the ArF excimer laser (193 nm), an ArF immersion lithography technique by exposure through water has been actively studied. However, the photolithography technique using light has been reaching its limit. Hence, an EUV lithography technique using EUV (a wavelength of 13.5 nm) has been drawing attention as a new lithography technique subsequent to the ArF immersion lithography technique.
In the production process of devices employing EUV lithography, adverse effects caused by an underlying substrate or EUV raise problems that, for example, a resist pattern for the EUV lithography is made into a skirt shape or an undercut shape, thus a favorable straight resist pattern cannot be formed, and a sensitivity to EUV is too low to achieve sufficient throughput. Thus, the EUV lithography process does not require the resist underlayer film (bottom anti-reflective coating) having the anti-reflection properties, but requires a resist underlayer film for EUV lithography so as to reduce these adverse effects, to form a favorable straight resist pattern, and to improve the resist sensitivity.
On the resist underlayer film for EUV lithography, a resist is applied after the film formation. Thus, as with the bottom anti-reflective coating, the resist underlayer film for EUV lithography requires the characteristics of no intermixing with the resist layer (being insoluble in a resist solvent) and no diffusion of a low molecular weight compound from a bottom anti-reflective coating material into a resist applied on the bottom anti-reflective coating during application or drying by heat.
In the generation using the EUV lithography, the resist pattern has an extremely small width, and hence the resist for EUV lithography is required to be a thinner film. To address this, the time for a removal process of an organic bottom anti-reflective coating by etching is required to be significantly reduced, and this requires a resist underlayer film for EUV lithography that can be used as a thin film or a resist underlayer film for EUV lithography that provides a large selection ratio of the etching rate with respect to that of a resist for EUV lithography.